Scientists Are Turning Human Excrement Into Renewable Biofuel

A team of researchers from Israel has demonstrated, for the first time, a technique for converting human excrement into hydrochar—a safe, renewable biomass fuel (like the example above) that resembles charcoal—as well as a nutrient-rich fertilizer.Photo: iStock

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A team of researchers from Israel’s Ben Gurion University of the Negev (BGU) has demonstrated, for the first time, a technique for converting human excrement into hydrochar—a safe, renewable biomass fuel that resembles charcoal—as well as a nutrient-rich fertilizer.

According to the team, this process could potentially address two major issues that affect many less-affluent countries—poor sanitation and growing energy needs.

While access to waste treatment worldwide has improved significantly in recent years, approximately 2.3 billion people still lack basic sanitation services, according to the World Health Organization. Of those, around 892 million people—most of whom live in rural areas—defecate in the open.

"Human excreta are considered hazardous due to their potential to transmit disease," Amit Gross, from the Department of Environmental Hydrology and Microbiology at BGU, said in a statement. "While it is rich in organic matter nutrients such as nitrogen, phosphorus and potassium, human waste also contains micropollutants from pharmaceuticals, which can lead to environmental problems if not disposed or reused properly."

Energy scarcity is also a problem in these regions: Approximately 2 billion people worldwide use solid biomass—such as wood—which is converted into charcoal and then used for cooking and heating. However, these practices have a significant impact on the environment, contributing to air pollution, greenhouse gas emissions, deforestation and soil erosion.

In a pilot study published in the Journal of Cleaner Production, the researchers described how they used a technique known as “hydrothermal carbonization” to heat raw solid human waste in a special “pressure cooker” to three different temperatures (180, 210 and 240 degrees Celsius) for periods of either 30, 60 or 120 minutes.

This sterilizes the human waste and dries it out, creating a solid coal-like substance known as hydrochar.

“Basically, we are mimicking coal formation in nature in much shorter time,” Gross said. “In these conditions, different chemical reactions occur and the wet biomass is converted into a hydrochar, a coal-like material that is rich in carbon and can potentially be used as an energy source.”

In addition, a nutrient-rich liquid is produced that could be used as a fertilizer. The latest study builds on a similar technique that the BGU team demonstrated last year for treating wet biomass, such as poultry excrement.

According to the researchers, the paper contains a number of key findings.

“This is the first study to have used actual human excreta in its “natural” moisture content,” Gross said. “We found that temperature had the biggest influence on the hydrochar characteristics (in comparison to reaction time). The generated hydrochar had energy content similar to coal used for electricity production. We also demonstrated that the results obtained at the laboratory are valid at a pilot scale reactor, reflecting that it may be straightforward to upscale.”

“Our dream is that people will use this technology in public toilets as a decentralized solution," he said.